1. Field of the Invention
The present invention generally relates to a needle assembly for a hypodermic syringe, and more particularly to a needle assembly for a hypodermic syringe wherein the quantity of liquid medicine left in a needle holder and a snout hole of a syringe when the injection has been completed, is made extremely small.
2. Description of the Prior Art
In general, a needle assembly for a hypodermic syringe comprises a pointed needle and a needle holder which receives the needle at its one end. The needle holder is a hollow tubular member and is made flared from the needle receiving section towards its opposite open end so as to form a flared bore therein. This bore is shaped and sized to be tightly fitted over an externally tapered snout of a syringe in a manner so-called Leur taper coupling. In order to ensure the more tight gripping of the needle holder and the snout, it is necessary to leave a room in the bore between the free end of the tapered snout and the innermost end wall of the bore for allowing the snout to be further pushed forward if desired, even when the needle holder has been press fitted on the snout.
In the prior needle assembly, however, since a space including the room in the bore of the needle holder is left free and a snout hole of the syringe is left free also, there is a disadvantage that some extent of liquid medicine remains in the needle holder and in the snout hole, even when a plunger has been pressed to the maximum against the end wall of the syringe bore so as to force the liquid medicine completely out of the syringe bore. Such loss of the remaining liquid medicine can not be ignored and is worth due consideration, particularly when the liquid medicine is an expensive one, such as insulin etc. Further, there is another disadvantage in the prior art needle assembly that impurities enter in the liquid medicine in the syringe bore and are consequently introduced in a human body, particularly when insulin is used wherein a patient himself is legally permitted to inject the same into his body. These impurities include not only a dust or fine particles floating in the air, but also fine fragments of glass which are produced when an ampoule is cut away.